Strap cell design for static random access memory (sram) array

ABSTRACT

A static random access memory (SRAM) array is provided. The SRAM array includes a first bit cell array, a second bit cell array, and a strap cell. The second bit cell array is arranged along a first direction. The strap cell is arranged along a second direction and is positioned between the first bit cell array and the second bit cell array along the first direction. The strap cell includes an H-shaped NW region, an H-shaped PW region, and a deep N-type well (DNW) region. The H-shaped NW region and the H-shaped PW region each includes two strip portions extending along the first direction and a linking portion extending along the second direction. Two terminals of the linking portion are in contact with the two strip portions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/564,393, filed Sep. 28, 2017, the entirety of which is incorporatedby reference herein.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs where each generation has smaller and more complexcircuits than the previous generation. However, these advances haveincreased the complexity of processing and manufacturing ICs and, forthese advances to be realized, similar developments in IC processing andmanufacturing are needed. In the course of IC evolution, functionaldensity (i.e., the number of interconnected devices per chip area) hasgenerally increased while geometric size (i.e., the smallest componentthat can be created using a fabrication process) has decreased.

Static Random Access Memory (SRAM) is commonly used in integratedcircuits. SRAM cells have the advantageous feature of being able to holddata without the need for refreshing. With the increasingly demandingrequirements on the speed of integrated circuits, the read speed andwrite speed of SRAM cells have also become more important. With theincreasing down-scaling of the already very small SRAM cells, however,such requests are difficult to achieve. For example, the sheetresistance of metal lines, which form the word-lines and bit-lines ofSRAM cells, becomes higher, and hence the RC delay of the word lines andbit-lines of SRAM cells is increased, preventing any substantialimprovements in the read speed and write speed.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It shouldbe noted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a block diagram of an SRAM array in accordance withsome embodiments;

FIG. 2 illustrates circuit diagrams of a static random access memory(SRAM) cell in accordance with some embodiments;

FIG. 3 illustrates circuit diagrams of a static random access memory(SRAM) cell in accordance with some embodiments;

FIG. 4 is a perspective view of a fin field-effect transistor (FinFET)in accordance with some embodiments;

FIG. 5 illustrates a layout of a SRAM unit cell in an SRAM array inaccordance with embodiments;

FIGS. 6A and 6B illustrate layouts of an SRAM array in accordance withsome embodiments;

FIG. 7A illustrates a cross-sectional views taken along line A1-A1′ ofFIG. 6A;

FIG. 7B illustrates a cross-sectional views taken along line A2-A2′ ofFIG. 6A;

FIG. 8A illustrates a cross-sectional views taken along line B1-B1′ ofFIG. 6A;

FIG. 8B illustrates a cross-sectional views taken along line B2-B2′ ofFIG. 6A; and

FIG. 9 illustrates a layout of an SRAM array in accordance with someembodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows includes embodiments in which the first and second features areformed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact.The present disclosure may repeat reference numerals and/or letters insome various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between somevarious embodiments and/or configurations discussed.

Furthermore, spatially relative terms, such as “beneath,” “below,”“lower,” “above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Some embodiments of the disclosure are described. Additional operationscan be provided before, during, and/or after the stages described inthese embodiments. Some of the stages that are described can be replacedor eliminated for different embodiments. Additional features can beadded to the semiconductor device structure. Some of the featuresdescribed below can be replaced or eliminated for different embodiments.Although some embodiments are discussed with operations performed in aparticular order, these operations may be performed in another logicalorder.

The fins may be patterned using any suitable method. For example, thefins may be patterned using one or more photolithography processes,including double-patterning or multi-patterning processes. Generally,double-patterning or multi-patterning processes combine photolithographyand self-aligned processes, allowing patterns to be created that have,for example, pitches smaller than what is otherwise obtainable using asingle, direct photolithography process. For example, in one embodiment,a sacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-alignment process. The sacrificial layeris then removed, and the remaining spacers may then be used to patternthe fins.

A static random access memory (SRAM) cell and the corresponding SRAMcell structure (e.g. a SRAM array) are provided in accordance withvarious exemplary embodiments. Some variations of some embodiments arediscussed. Throughout the various views and illustrative embodiments,like reference numbers are used to designate like elements.

FIG. 1 illustrates a block diagram of a SRAM array 600 in accordancewith some embodiments. In some embodiments, the SRAM array 600 includesa bit cell array 602A, a bit cell array 602B, a strap cell 604 and edgeSRAM cells 606 and 608.

In some embodiments, the SRAM bit cell arrays 602A and 602B are arrangedalong a column direction (i.e. a direction 302). In some embodiments,each of the bit cell arrays 602A and 602B includes a plurality of SRAMcells 500, for example, functional SRAM cells. The SRAM cells 500 of thebit cell arrays 602A and 602B may be configured to be electricallyconnected to control circuits 610A and 610B. In some embodiments, theSRAM array 600 includes the SRAM cells 500 having a six port SRAMcircuit layout with six transistors. In some other embodiments, the SRAMarray 600 includes the SRAM cells 500 having a different number ofports, such as an eight port SRAM circuit layout, and variousembodiments are not limited to a particular memory cell circuit.

In some embodiments, each of the SRAM cells 500 in each of the bit cellarrays 602A and 602B are arranged in rows (along a direction 300) andcolumns (along the direction 302). For example, the columns of the SRAMcells 500 in each of the bit cell arrays 602A and 602B may be arrangedin the direction 302. As shown in FIG. 1, each of the bit cell arrays602A and 602B may include N columns, where N is a positive integer, inaccordance with some embodiments. For example, the rows of the SRAMcells 500 in each of the bit cell arrays 602A and 602B may be arrangedin the direction 300 that is different than the direction 302. As shownin FIG. 1, each of the bit cell arrays 602A and 602B may include M rows,where M is a positive integer, in accordance with some embodiments. Forexample, each of the bit cell arrays 602A and 602B may include fourcolumns and eight rows (denoted as “4×8” SRAM cells) as shown in FIG. 1.Therefore, each of the bit cell arrays 602A and 602B may include, forexample, 64×64 SRAM cells, 128×128 SRAM cells, 256×256 SRAM cells, orthe like. The number of SRAM cells in the bit cell array 602A may be thesame or different than the number of SRAM cells in the bit cell array602B.

Each of the SRAM cells 500 in the SRAM array 600 includes a bit lineportion BL extending in the direction 302, a complementary bit lineportion BLB extending in the direction 302, a word line portion wordline (WL) (e.g. a WL 122 shown in FIGS. 2 and 3) extending in thedirection 300, a connection to a first voltage line Vss (not shown), anda connection to second voltage line Vdd (not shown). In someembodiments, the SRAM cells 500 arranged in the same column along thedirection 302 (i.e. the column direction) share a common bit line (BL)(e.g. a BL 114A and a BL 114B) and a common bit line bar (BLB) (e.g. aBLB 116A and a BLB 116B). For example, each of the SRAM cells 500 in thesame column in the bit cell array 602A (or the bit cell array 602B)includes a portion of a BL and a BLB, which when combined with otherSRAM cells 500 in the column in the bit cell array 602A (or the bit cellarray 602B) forms continuous conductive lines (the BL and the BLB). Inaddition, the SRAM cells 500 arranged in the same row along thedirection 300 may share a common word line (WL). The BLs 114A (or 114B)and the BLBs 116A (or 116B) may be electrically connected to the controlcircuits 610A (or 610B), which may activate certain the BLs 114A (or114B) and/or the BLBs 116A (or 116B) to select a particular column inthe SRAM array 600 for read and/or write operations. In someembodiments, the control circuits 610A and 610B further includeamplifiers to enhance a read and/or write signal. For example, thecontrol circuits 610A and 610B may include selector circuitry, drivercircuitry, sense amplifier (SA) circuitry, combinations thereof, and thelike.

In some embodiments, the strap cell 604 arranged along the direction 300(i.e. the row direction) and positioned between the bit cell arrays 602Aand 602B along the direction 302 (i.e. the column direction). The strapcell 604 may help to make the performance of the SRAM array 600 moreuniform among the inner cells and the edge cells of the SRAM array. Forexample, the strap cell 604 of the SRAM array 600 may include bothN-type well (NW) regions that make an electrical connection between avoltage line and an NW region in a substrate, and P-type well (PW)regions that make an electrical connection between a voltage line and aPW region in a substrate. These connections are used to help withuniform charge distribution throughout the SRAM array. The layout of thestrap cell 604 may be described in greater detail below using thefollowing figures (e.g. FIG. 6A, FIG. 6B, FIG. 7A, FIG. 7B, FIG. 8A,FIG. 8B and FIG. 9).

In some embodiments, the edge (dummy) cells 606 and 608 are arrangedaround a periphery of the bit cell arrays 602A and 602B and the strapcell 604. Each of the edge (dummy) cells 606 and 608 may include a dummySRAM cell. The arrangement of the dummy SRAM cell may be the same orsimilar to the SRAM cell 500. In addition, the dummy SRAM cell may notperform any circuit function. The edge cells 606 and 608 may have anysuitable configuration and may be included for improved uniformity offins and/or metal features. For example, each column of the bit cellarrays 602A and 602B and the strap cell 604 may begin and end with theedge cell 606. For example, each row of the bit cell arrays 602A and602B and the strap cell 604 may begin and end with the edge cell 608.For example, the edge cells 606 may be equal in quantity to a quantityof columns of the bit cell arrays 602A (or 602B) in the SRAM array 600.In addition, the edge cells 608 may be equal in quantity to a quantityof rows of the bit cell arrays 602A and 602B in the SRAM array 600.

FIG. 2 illustrates a circuit diagram of SRAM cell 500 in accordance withsome embodiments. FIG. 3 illustrates an alternative circuit diagram ofthe SRAM cell 500 in accordance with some embodiments. Each of the SRAMcells 500 in the SRAM array 600 shown in FIG. 1 may have a circuitlayout shown in FIG. 2 and FIG. 3. For example, FIG. 2 and FIG. 3 mayillustrate a six port SRAM circuit layout with six transistors. OtherSRAM circuit layouts may be used in some other embodiments.

In some embodiments, the SRAM cell 500 includes pass-gate transistorsPG-1 and PG-2, pull-up transistors PU-1 and PU-2 and pull-downtransistors PD-1 and PD-2, as shown in FIG. 2. The pass-gate transistorsPG-1 and PG-2 and pull-up transistors PU-1 and PU-2 are p-typemetal-oxide-semiconductor (PMOS) transistors. The pull-down transistorsPD-1 and PD-2 are n-type metal-oxide-semiconductor (NMOS) transistors.The gates of the pass-gate transistors PG-1 and PG-2 are connected to,and controlled by, a word-line (WL) 122 that determines whether SRAMcell 500 is selected or not. A latch formed of the pull-up transistorsPU-1 and PU-2 and the pull-down transistors PD-1 and PD-2 stores a bit,and the complementary values of the bit are stored in storage node 110and storage node 112. The stored bit can be written into, or read from,the SRAM cell 500 through a bit-line (BL) 114 and a bit-line Bar (BLB)116. In addition, the BL 114 and the BLB 116 may carry complementarybit-line signals. In some embodiments, the SRAM cell 500 is poweredthrough a positive power supply node Vdd that has a positive powersupply voltage (also denoted as Vdd). The SRAM cell 500 is alsoconnected to power supply voltage Vss (also denoted as Vss), which maybe an electrical ground. In some embodiments, the pull-up transistorPU-1 and the pull-down transistor PD-1 collectively form a firstinverter. The pull-up transistor PU-2 and the pull-down transistor PD-2may collectively form a second inverter. The input of the first inverteris connected to the pass-gate transistor PG-1 and the output of thesecond inverter. In addition, the output of the first inverter isconnected to pass-gate transistor PG-2 and the input of the secondinverter.

The sources of the pull-up transistors PU-1 and PU-2 are connected to apower supply voltage-node (CVdd-node) 102 and a CVdd-node 104,respectively, which are further connected to power supply voltage Vddthrough a power supply voltage (CVdd) line 124. The power supply voltageVdd may be carried by a metal line. The sources of the pull-downtransistors PD-1 and PD-2 are connected to a power supply voltage-node(CVss-node) 106 and a CVss-node 108, respectively, which are furtherconnected to power supply voltage Vss through a power supply voltage(CVss) line 126. The power supply voltage Vss may be carried by a metalline. The gates of the pull-up transistor PU-1 and the pull-downtransistor PD-1 are connected to the drains of the pull-up transistorPU-2 and the pull-down transistor PD-2, in which the connection node isthe storage node 110. The gates of the pull-up transistor PU-2 and thepull-down transistor PD-2 are connected to the drains of the pull-downtransistor PU-1 and the pull-down transistor PD-1, in which theconnection node is the storage node 112. A source/drain region of thepass-gate transistor PG-1 is connected to the bit-line (BL) 114 at abit-line node 118. A source/drain region of the pass-gate transistorPG-2 is connected to the bit-line bar (BLB) 116 at a bit-line bar node120.

FIG. 3 illustrates an alternative circuit diagram of the SRAM cell 500in accordance with some embodiments. In some embodiments, the pull-uptransistor PU-1 and the pull-down transistor PD-1 shown in FIG. 1 arerepresented as a first inverter Inverter-1. In addition, the pull-uptransistor PU-2 and the pull-down transistor PD-2 are represented as asecond inverter Inverter-2. In some embodiments, the second inverterInverter-2 is cross-latched with the first inverter Inverter-1. Morespecifically, the output of the first inverter Inverter-1 is connectedto the pass-gate transistor PG-1 and the input of the second inverterInverter-2. The output of the second inverter Inverter-2 is connected tothe pass-gate transistor PG-2 and the input of the second inverterInverter-2.

FIG. 4 illustrates a perspective view of a fin field effect transistor(FinFET) 250, which may serve as any of the transistors in the SRAM cell500, including the pull-up transistor PU-1, the pull-up transistor PU-2,the pull-down transistor PD-1, the pull-down transistor PD-2, thepass-gate transistor PG-1, and the pass-gate transistor PG-2. In someembodiments, the FinFET 250 includes a semiconductor fin 204, a gatestructure 215, spacers 218, a drain region 220 and a source region 222.The semiconductor fin 204 extends above a semiconductor substrate 200.In some embodiments, the semiconductor substrate 200 and thesemiconductor fin 204 are made of the same material. For example, thesubstrate is a silicon substrate. In some instances, the substrateincludes a suitable elemental semiconductor, such as germanium ordiamond; a suitable compound semiconductor, such as silicon carbide,gallium nitride, gallium arsenide, or indium phosphide; or a suitablealloy semiconductor, such as silicon germanium, silicon tin, aluminumgallium arsenide, or gallium arsenide phosphide. In some embodiments,the substrate is a silicon on insulator (SOI) layer substrate or asilicon on sapphire (SOS) substrate. In some embodiments, thesemiconductor substrate 200 and the semiconductor fin 204 are made ofdifferent materials.

In some embodiments, the semiconductor fin 204 of the FinFET 250 may besurrounded by isolating features 206 formed on opposite sides of thesemiconductor fin 204. The isolating features 206 may electricallyisolate an active region (not shown) of the FinFET 250 from other activeregions. In some embodiments, the isolating features 206 are shallowtrench isolation (STI), field oxide (FOX), or another suitableelectrically insulating structure. For example, the semiconductor fin204 represents semiconductor fins 204-1, 204-2, 204-3 and 204-4 in alayout of the SRAM cell 500 shown in FIG. 5.

In some embodiments, the gate structure 215, which includes a gatedielectric 212 and a gate electrode 214 formed over the gate dielectric212, is positioned over sidewalls and a top surface of the semiconductorfin 204. Therefore, a portion of the semiconductor fin 204 overlaps thegate structure 215 may serve as a channel region of the FinFET 250. Insome embodiments, the channel region of p-type FinFETs, for example, thepull-up transistor PU-1 and the pull-up transistor PU-2, the channelregion include a SiGe channel region. In addition, the Ge concentrationin the SiGe channel region is in a range from about 10 at % to about 40at %. In some embodiments, the gate dielectric 212 is a high dielectricconstant (high-k) dielectric material. A high-k dielectric material hasa dielectric constant (k) higher than that of silicon dioxide. Examplesof high-k dielectric materials include hafnium oxide, zirconium oxide,aluminum oxide, silicon oxynitride, hafnium dioxide-alumina alloy,hafnium silicon oxide, hafnium silicon oxynitride, hafnium tantalumoxide, hafnium titanium oxide, hafnium zirconium oxide, another suitablehigh-k material, or a combination thereof. In some embodiments, the gateelectrode 214 is made of a conductive material, such as aluminum (Al),copper (Cu), tungsten (W), titanium (Ti), tantalum (Ta), or anotherapplicable material.

In some embodiments, the spacers 218 of the FinFET 250 are positionedover sidewalls and a top surface of the semiconductor fin 204. Inaddition, the spacers 218 may be formed on opposite sides of the gatestructure 215. In some embodiments, the spacers 218 are made of siliconnitride, silicon oxynitride, silicon carbide, another suitable material,or a combination thereof.

In some embodiments, portions of the semiconductor fin 204 that are notcovered by the gate structure 215 and the spacers 218 serve as a drainregion 220 and a source region 222. In some embodiments, the drainregion 220 and the source region 222 of p-type FinFETs, for example, thepass-gate transistor PG-1, the pass-gate transistor PG-2, the pull-uptransistor PU-1 and the pull-up transistor PU-2 are formed by implantingthe portions of the semiconductor fin 204 that are not covered by thegate structure 215 and the spacers 218 with a p-type impurity such asboron, indium, or the like. In some embodiments, the drain region 220and the source region 222 of n-type FinFETs, for example, the pull-downtransistor PD-1 and the pull-down transistor PD-2 are formed byimplanting the portions of the semiconductor fin 204 that are notcovered by the gate structure 215 and the spacers 218 with an n-typeimpurity such as phosphorous, arsenic, antimony, or the like.

In some embodiments, the drain region 220 and the source region 222 areformed by etching portions of the semiconductor fin 204 that are notcovered by the gate structure 215 and the spacers 218 to form recesses,and growing epitaxial regions in the recesses. The epitaxial regions maybe formed of Si, Ge, SiP, SiC, SiPC, SiGe, SiAs, InAs, InGaAs, InSb,GaAs, GaSb, InAlP, InP, C, or a combination thereof. Accordingly, inFIG. 3, the drain region 220 and the source region 222 may be formed ofsilicon germanium (SiGe) in some exemplary embodiments, while theremaining semiconductor fin 204 may be formed of silicon. In someembodiments, p-type impurities are in-situ doped in the drain region 220and the source region 222 during the epitaxial growth of the drainregion 220 and the source region 222 of the p-type FinFET 250, forexample, the pass-gate transistor PG-1, the pass-gat transistor PG-2,the pull-up transistor PU-1 and the pull-up transistor PU-2. Inaddition, n-type impurities are in-situ doped in the drain region 220and the source region 222 during the epitaxial growth of the drainregion 220 and the source region 222 of the n-type FinFET 250, forexample, the pull-down transistor PD-1 and the pull-down transistorPD-2.

In some other embodiments, the pass-gate transistors PG-1 and PG-2,pull-up transistors PU-1 and PU-2, and pull-down transistors PD-1 andPD-2 of the SRAM cell 500 are planar MOS devices.

FIG. 5 illustrates the layout of the SRAM cell 500 in each of the bitcell arrays 602A and 602B in the SRAM array 600 (FIG. 1) in accordancewith embodiments. The SRAM cell 500 may serve as a SRAM unit cell.

In some embodiments, the SRAM cell 500 is arranged in an array in eachof the bit cell arrays 602A and 602B (FIG. 1) including a plurality ofrows and a plurality of columns. In addition, the SRAM cells 500 may bearranged in the same row with a pitch P1 in the direction 300 (the rowdirection). Furthermore, the SRAM cells 500 may be arranged in the samecolumn as a pitch P2 in the direction 302 (the column direction). Theadjacent two SRAM cells 500 are arranged in mirror symmetry. An outerboundary 250 of each of the SRAM cells 500 is illustrated using dashedlines, which mark a rectangular region. An NW region 252 may be arrangedat the middle of the SRAM cell 500. In addition, two PW regions 254 maybe arranged on opposite sides of the NW region 252 along the direction302. Furthermore, the CVdd-node 102, the CVdd-node 104, the CVss-node106, the CVss-node 108, the BL node 118 and the BLB node 120, which areshown in FIG. 2, are also illustrated in FIG. 5.

In some embodiments, as shown in FIG. 5, the SRAM cell 500 includes thepass-gate fin field-effect transistors (FinFETs) PG-1 and PG-2, thepull-up FinFETs PU-1 and PU-2, and the pull-down FinFETs PD-1 and PD-2formed by arranging four separate gate electrode patterns 215-1, 215-2,215-3 and 215-4 on the four semiconductor fins 204-1, 204-2, 204-3 and204-4.

In some embodiments, as shown in FIG. 5, the semiconductor fins 204-1,204-2, 204-3 and 204-4 are arranged along the direction 300 (e.g. therow direction shown in FIG. 1) and extend along the direction 302 (e.g.the column direction shown in FIG. 1) that is different from direction300. For example, direction 302 is substantially perpendicular todirection 300. In some embodiments, direction 302 serves as thelongitudinal direction of semiconductor fins 204-1, 204-2, 204-3 and204-4.

In some embodiments, as shown in FIG. 5, the gate electrode patterns215-1, 215-2, 215-3 and 215-4 are strip (line) shapes extendingsubstantially along the direction 300. For example, the gate electrodepattern 215-1 may be positioned overlying the semiconductor fin 204-1,the semiconductor fin 204-2 and extends to cover an end portion of thesemiconductor fin 204-3. The gate electrode pattern 215-2 may bepositioned overlying the semiconductor fin 204-3 and the semiconductorfin 204-4 and may extend to cover an end portion of the semiconductorfin 204-2. The gate electrode pattern 215-3 may be positioned overlyingthe semiconductor fin 204-1. In addition, the gate electrode pattern215-4 may be positioned overlying the semiconductor fin 204-4.

In some embodiments, as shown in FIG. 5, the gate electrode pattern215-1 forms the pull-down FinFET PD-1 with the underlying semiconductorfin 204-1 (in the PW region 254 on the left side of the NW region 252).In addition, the gate electrode pattern 215-1 may form the pull-upFinFET PU-1 with the underlying semiconductor fin 204-2 (in the NWregion 252). The gate electrode pattern 215-2 forms the pull-down FinFETPD-2 with the underlying semiconductor fin 204-4 (in the PW region 254on the right side of the NW region 252). In addition, the gate electrodepattern 215-2 forms the pull-up FinFET PU-2 with the underlyingsemiconductor fin 204-3 (in the NW region 252). The gate electrodepattern 215-3 forms the pass-gate FinFET PG-1 with the underlyingsemiconductor fin 204-1, which is the same semiconductor fin that alsoforms the pull-down FinFET PD-1. The gate electrode pattern 215-4 formsthe pass-gate FinFET PG-2 with the underlying semiconductor fin 204-4,which is the same semiconductor fin that also forms the pull-down FinFETPD-2.

In some embodiments, the gate electrode pattern 215-1 of the pull-upFinFET PU-1 and the pull-down FinFET PD-1 is aligned to the gateelectrode pattern 215-4 of the pass-gate FinFET PG-2 substantially alongthe direction 300. In addition, the gate electrode pattern 215-2 of thepull-up FinFET PU-2 may be aligned to the pull-down FinFET PD-2 and thegate electrode pattern 215-3 of the pass-gate FinFET PG-1 substantiallyalong the direction 300.

In some embodiments, the gate electrode pattern 215-1 of the pull-downFinFET PD-1 and the pull-up FinFET PU-1, the gate electrode pattern215-2 of the pull-down FinFET PD-2 and the pull-up FinFET PU-2 arepositioned within a boundary 250 of the SRAM cell 500. In addition, thegate electrode patterns 215-3 of the pass-gate FinFETs PG-1 of the twoadjacent SRAM cells may be in contact with each other. Similarly, thegate electrode patterns 215-4 of the pass-gate FinFETs PG-2 of the twoadjacent SRAM cells may be in contact with each other.

FIGS. 6A and 6B illustrate layouts each including an N-type well (NW)region 252, a P-type well (PW) region 254 and a deep N-type well (DNW)region 680 in a portion of the SRAM array 600 in accordance with someembodiments. FIGS. 6A and 6B illustrate the arrangement of thesemiconductor fins 204. In addition, the arrangements of the NW regionsand the PW regions in the strap cell 604 illustrated in FIGS. 6A and 6Bmay be the same but labeled in different reference signs for thefollowing detailed description. For example, the strap cell 604 shown inFIGS. 6A and 6B may serve as a strap unit cell. The width of the strapcell 604 along the direction 300 may be the same to four times of thepitch P1 of the SRAM cells 500 (i.e. W=4P1). The length L of the strapcell 604 along the direction 302 may be the same to three times of thepitch P2 of the SRAM cells 500 (i.e. L=3P1). Furthermore, FIGS. 6A and6B merely illustrate a portion the bit cell array 602A and a portion ofthe bit cell array 602B (e.g., four columns and four rows) for the sakeof the convenience. Moreover, the edge SRAM cells 606 and 608 (FIG. 1)of the SRAM array 600 are not shown in FIGS. 6A and 6B.

In some embodiments, the strap cell 604 includes an H-shaped NW region660 and an H-shaped PW region 670 in a view along the direction 300 of aplan view as shown in FIG. 6A. The H-shaped PW region 670 may bepositioned adjacent to (next to) the H-shaped NW 660 region along thedirection 300 (e.g. the row direction). In some embodiments, theH-shaped NW region 660 includes two strip portions 662-1 and 662-2 and alinking portion 664. The strip portions 662-1 and 662-2 may bepositioned extending along the direction 302 (e.g. the columndirection). In addition, the linking portion 664 may be positionedextending along the direction 300 (e.g. the row direction). Furthermore,two terminals 664-1 and 664-2 of the linking portion 664 may be incontact with the two strip portions 662-1 and 662-2. Similarly, theH-shaped PW region 670 may include two strip portions 672-1 and 672-2and a linking portion 674. The strip portions 672-1 and 672-2 may bepositioned extending along the direction 302 (e.g. the columndirection). In addition, the linking portion 674 may be positionedextending along the direction 300 (e.g. the row direction). Furthermore,two terminals 674-1 and 674-2 of the linking portion 674 may be incontact with the two strip portions 672-1 and 672-2. In someembodiments, the strip portion 662-1 of the H-shaped NW region 660 is incontact with the strip portion 672-1 of the H-shaped PW region 670.

In some embodiments, the strap cell 604 further includes a PW region 676and a PW region 677 adjacent to opposite sides of the linking portion664 of the H-shaped NW region 660 along the direction 302 (e.g. thecolumn direction) in the plan view as shown in FIG. 6A. In addition, thestrap cell 604 may include an NW region 666 and an NW region 667adjacent to opposite sides of the linking portion 674 of the H-shaped PWregion 670 along the direction 302 (e.g. the column direction).

The strip portions 662-1 and 662-2 of the H-shaped NW region 660 mayhave the same width W1 along the direction 300. The strip portions 672-1and 672-2 of the H-shaped PW region 670 may have the same width W2 alongthe direction 300. In addition, the width W1 of the strip portion 662-1(or 662-2) of the H-shaped NW region 660 may be less than the width W2of the strip portion 672-1 (or 672-2) of the H-shaped PW region 670. Forexample, the width W2 may be two times as large as the width W1 (becausethe PW regions of the adjacent SRAM cells in the direction 300 may bemerged together and have a width W2, the width of the merged PW regionof the adjacent SRAM cells may be two times as large as the width of theNW region of each of the adjacent SRAM cells).

The strap cell 604 may include a T-shaped PW region 678 arrangedadjacent to the strip portion 672-1 of the H-shaped PW region 670, asshown in FIG. 6A in accordance with some embodiments. The T-shaped PWregion 678 and the linking portion 674 of the H-shaped PW region 670 maybe positioned on opposite sides of the strip portion 672-1 of theH-shaped PW region 670, along the direction 300. For example, theT-shaped PW region 678 may include a horizontal portion 678-1 along thedirection 302 and a vertical portion 678-2 along the direction 300. Thevertical portion 678-2 may be positioned between the horizontal portion678-1 and the strip portion 672-1. In addition, NW regions 668 and 669may be positioned on opposite sides of the vertical portion 678-2 alongthe direction 302. Furthermore, the horizontal portion 678-1 and thevertical portion 678-2 may have the same widths W1 along the direction300.

The strap cell 604 may include a strip-shaped PW region 679 adjacent tothe strip portion 662-1 of the H-shaped NW region 660, as shown in FIG.6 in accordance with some embodiments. The strip-shaped PW region 679may extend along the direction 302. In addition, the strip-shaped PWregion 679 and the linking portion 664 of the H-shaped NW region 660 maybe positioned on opposite sides of the strip portion 662-1 of theH-shaped PW region 670, along the direction 300. The strip-shaped PWregion 679 may have a width W1 along the direction 300.

In some embodiments, the strap cell 604 further includes a deep N-typewell (DNW) region 680 underlying the H-shaped NW region 660, the NWregion 666, 667, 668 and 669, the H-shaped PW region 670, the PW regions676 and 677, the T-shaped PW region 678 and the strip-shaped PW region679. In addition, a boundary 681 of the DNW region 680 may surround aboundary of the strap cell 604. Portions of the boundary 681 of the DNWregion 680 along the direction 300 may be positioned in the within thebit cell array 602A and the bit cell array 602B.

In some embodiments, the bit cell array 602A and the bit cell array 602Beach includes NW regions 252 and PW regions 254 extending along thedirection 302 (e.g. the column direction). In addition, the NW regions252 and the PW regions 254 may be arranged alternately along thedirection 300 (e.g. the row direction). For example, the bit cell array602A and the bit cell array 602B may each include four columns (e.g.,Column 1, Column 2, Column 3 and Column 4), which allows four SRAM cells500 (FIG. 5) to be arranged in the same row along the direction 300.Therefore, the PW regions of the adjacent SRAM cells in the direction300 may be merged together to form the PW region 254 having the widthW2. The width W2 of the PW region 254 may be two times larger than thewidth W1 of the NW region 252. In addition, the pitch P1 of the SRAMcells 500 (FIG. 5) may be equal to the total width of the PW region 254(W2) and the NW region 252 (W1) along the direction 300. Furthermore,the total width of the H-shaped NW region 660 and the H-shaped PW region670 along the row direction may be three times as long as the pitch P1of the SRAM cells 500 (FIG. 5).

In some embodiments, the strip portions 662-1 and 662-2 of the H-shapedNW region 660 of the strap cell 604 are respectively in direct contactwith the corresponding NW regions 252 in the bit cell array 602A and thebit cell array 602B. In addition, the NW regions 666, 667, 668 and 669of the strap cell 604 may be respectively in direct contact with the NWregions 252 in the bit cell array 602A and the bit cell array 602B. Thestrip portions 672-1 and 672-2 of the H-shaped PW region 670, thehorizontal portion 678-1 of the T-shaped PW region 678 and thestrip-shaped PW region 679 of the strap cell 604 may be respectively indirect contact with the corresponding PW regions 254 in the bit cellarray 602A and the bit cell array 602B. Furthermore, the PW regions 676and 677 of the strap cell 604 may be respectively in direct contact withthe corresponding PW regions 254 in the bit cell array 602A and the bitcell array 602B.

The layout of the PW regions and the NW regions in the strap cell 604may be represented in other ways shown in FIG. 6B, in accordance withsome embodiments. In some embodiments, the strap cell 604 includes afirst strap column 630, a second strap column 632, a third strap column634, a fourth strap column 636, a fifth strap column 638 and a sixthstrap column 640 arranged along the direction 300 and extending alongthe direction 302 in the plan view shown in FIG. 6B. The first strapcolumn 630, the second strap column 632, the third strap column 634, thefourth strap column 636, the fifth strap column 638 and the sixth strapcolumn 640 may each have a length L along the direction 302. Inaddition, the strap cell 604 may include a first strap row 642, a secondstrap row 644 and a third strap row 646 arranged along the direction 302and extending along the direction 300. The length of the first strap row642, the second strap row 644 and the third strap row 646 may each bethree time less than the length L of each of the strap columns (630,632, 634, 636, 638 and 640) of the strap cell 604.

Please refer to FIGS. 6A and 6B, the first strap column 630 (FIG. 6B)includes the linking portion 674 of the H-shaped PW region 670 (i.e. thePW region) and the NW regions 666 and 667 (FIG. 6A). The linking portion674 of the H-shaped PW region 670 may serve as a PW region 674 of thefirst strap column 630, in accordance with some embodiments. The NWregions 666 and 667 may be positioned on opposite sides of the PW region674 along the direction 302 (e.g. the column direction). The secondstrap column 632 (FIG. 6B) may include the strip portion 672-1 of theH-shaped PW region 670 (FIG. 6A). The strip portion 672-1 of theH-shaped PW region 670 may serve as a PW region 672-1 of the secondstrap column 632. In addition, the length of the PW region 672-1 isequal to the length L of the second strap column 632 along the direction302. The third strap column 634 (FIG. 6B) may include the strip portion672-2 of the H-shaped PW region 670 (FIG. 6A). The strip portion 672-2of the H-shaped PW region 670 may serve as a PW region 672-2 of thethird strap column 634. In addition, the length of the PW region 672-2is equal to the length L of the third strap column 634 along thedirection 302. Therefore, the PW region 674 of the first strap column630 may directly connect to the PW region 672-1 of the second strapcolumn 632 and the PW region 672-2 of the third strap column 634 to formthe H-shaped PW region 670 in the plan view shown in FIGS. 6A and 6B, inaccordance with some embodiments. The second strap column 632 and thethird strap column 634 may have the same width W2 that is greater thanthe width W1 of the first strap column 630 along the direction 300.

Please refer to FIGS. 6A and 6B, the fourth strap column 636 (FIG. 6B)includes the linking portion 664 of the H-shaped NW region 660 and thePW regions 676 and 677 (FIG. 6A). The linking portion 664 of theH-shaped NW region 660 may serve as an NW region 664 of the fourth strapcolumn 636, in accordance with some embodiments. The PW regions 676 and677 may be positioned on opposite sides of the NW region 664 along thedirection 302 (e.g. the column direction). The fifth strap column 638(FIG. 6B) may include the strip portion 662-1 of the H-shaped NW region660 (FIG. 6A). The strip portion 662-1 of the H-shaped NW region 660 mayserve as an NW region 662-1 of the sixth strap column 640. In addition,the length of NW region 662-1 is equal to the length L of the fifthstrap column 638. The sixth strap column 640 (FIG. 6B) may include thestrip portion 662-2 of the H-shaped NW region 660 (FIG. 6A). The stripportion 662-2 of the H-shaped NW region 660 may serve as the NW region662-2 of the sixth strap column 640. In addition, the length of NWregion 662-2 is equal to the length L of the sixth strap column 640.Therefore, the NW region 664 of the fourth strap column 636 may directlyconnect to the NW region 662-1 of the NW region 662-1 and the NW region662-2 of the sixth strap column 640 to form the H-shaped NW region 660in the plan view shown in FIGS. 6A and 6B, in accordance with someembodiments. The width W2 of the fourth strap column 636 may be greaterthan the width W1 of the fifth strap column 638 and of the sixth strapcolumn 640.

The strap cell 604 may further include a seventh strap column formed ofthe horizontal portion 678-1 of the T-shaped PW region 678 (FIG. 6A).The strap cell 604 may further include an eighth strap column formed ofthe vertical portion 678-2 of the T-shaped PW region 678, the NW regions668 and 669 (FIG. 6A). In addition, the eighth strap column may bepositioned between the seventh strap column and the second strap column632 along the direction 300. The strap cell 604 may further include aninth strap column formed of the strip-shaped PW region 679 (FIG. 6A).In addition, the ninth strap column may be positioned adjacent to thesixth strap column 640 along the direction 300.

Please refer to FIGS. 6A and 6B, the first strap row 642 (FIG. 6B) ofthe strap cell 604 includes the NW region 666, the NW region 668, aportion of the NW region 662-1, a portion of the NW region 662-2, aportion of the PW region 672-1, a portion of the PW region 672-2, the PWregion 676, a portion of the horizontal portion 678-1 of the T-shaped PWregion 678 and a portion of the strip-shaped PW region 679 (FIG. 6A), inaccordance with some embodiments. For example, the NW regions (the NWregion 666, the NW region 668, a portion of the NW region 662-1 and aportion of the NW region 662-2) and the PW regions (a portion of the PWregion 672-1, a portion of the PW region 672-2, the PW region 676, aportion of the horizontal portion 678-1 of the T-shaped PW region 678and a portion of the strip-shaped PW region 679) of the first strap row642 are arranged alternately along the direction 300 (the rowdirection). The PW regions 672-1 and 672-2 may be positioned on oppositesides of the NW region 666 along the direction 300. In addition, the NWregions 662-1 and 662-2 may be positioned on opposite sides of the PWregion 676 along the direction 300.

In some embodiments, the second strap row 644 (FIG. 6B) of the strapcell 604 is arranged adjacent to the first strap row 642. The secondstrap row 644 may include a strip-shaped PW region and a strip-shaped NWregion connected to the strip-shaped PW region and a portion of thestrip-shaped PW region 679 (FIG. 6A). For example, the strip-shaped PWregion of the second strap row 644 may include the PW region 674, aportion of the PW region 672-1 and a portion of the PW region 672-2, aportion of the horizontal portion 678-1 and the vertical portion 678-2of the T-shaped PW region 678. For example, strip-shaped NW region ofthe second strap row 644 may include the NW region 664, a portion of theNW region 662-1 and a portion of the NW region 662-2.

In some embodiments, the third strap row 646 (FIG. 6B) is arrangedadjacent to the second strap row 644. The arrangements of the PW regionsand the NW regions in the third strap row 646 may be the same or asimilar to those in the first strap row 642. For example, the thirdstrap row 646 (FIG. 6B) may include the NW region 667, the NW region669, a portion of the NW region 662-1, a portion of the NW region 662-2,a portion of the PW region 672-1, a portion of the PW region 672-2, thePW region 677, a portion of the horizontal portion 678-1 of the T-shapedPW region 678 and a portion of the strip-shaped PW region 679 (FIG. 6A).For example, the NW regions (the NW region 667, the NW region 669, aportion of the NW region 662-1 and a portion of the NW region 662-2) andthe PW regions (a portion of the PW region 672-1, a portion of the PWregion 672-2, the PW region 676, a portion of the horizontal portion678-1 of the T-shaped PW region 678 and a portion of the strip-shaped PWregion 679) of the third strap row 646 are arranged alternately alongthe direction 300 (the row direction). The PW regions 672-1 and 672-2may be positioned on opposite sides of the NW region 667 along thedirection 300. In addition, the NW regions 662-1 and 662-2 may bepositioned on opposite sides of the PW region 677 along the direction300.

FIGS. 7A and 7B illustrate cross-sectional views along lines A1-A1′ andA2-A2′ of FIG. 6A. In addition, FIGS. 7A and 7B illustrate therelationship between the positions of the DNW region 680, the NW regionsand the PW regions in the strap cell 604, the bit cell array 602A andthe bit cell array 602B along the direction 302 (the column direction).The DNW region 680 may be connected to discrete NW regions (the H-shapedNW region 660, the NW region 666, 667, 668 and 669) in the strap cell604 and overlaps the NW regions 252 in the bit cell array 602A and thebit cell array 602B (FIG. 6A). For example, the NW region 666 and the NWregion 667 in the strap cell 604 may be connected to each other throughthe DNW region 680 as shown in FIG. 7A. In addition, the NW region 252in the bit cell array 602A may be connected to the NW region 252 in thebit cell array 602B through the DNW region 680. Furthermore, the PWregions 254 may be positioned underlying the NW regions 252 and adjacentto opposite sides of the DNW region 680. For example, the NW region 664and the PW regions 676 and 677 in the strap cell 604 are positionedoverlying the DNW region 680 as shown in FIG. 7B. In addition, the PWregions 254 in the bit cell array 602A and the bit cell array 602B maybe positioned overlying the DNW region 680 and adjacent to oppositesides of the DNW region 680.

FIGS. 8A and 8B illustrate cross-sectional views along lines B1-B1′ andB2-B2′ of FIG. 6A. In addition, FIGS. 8A and 8B illustrate therelationship between the positions of the DNW region 680, the NW regionsand the PW regions in the strap cell 604, the bit cell array 602A andthe bit cell array 602B along the direction 300 (the row direction). Forexample, the DNW region 680 may be positioned underlying the NW region666, the NW region 667, the PW region 672-1 and the PW region 672-2 inthe strap cell 604 as shown in FIG. 8A. The NW region 666 and the NWregion 667 may be connected to each other through the DNW region 680. Inaddition, the NW region 666, the NW region 667, the PW region 672-1 andthe PW region 672-2 may be arranged alternately along the direction 300(the row direction). For example, the PW regions 254 may be connected toeach other and extending under the NW regions 252 in the bit cell array602A (or the bit cell array 602B) as shown in FIG. 8B. In addition, theNW regions 252 and the PW regions 254 may be arranged alternately alongthe direction 300 (the row direction).

FIG. 9 illustrates layouts of heavily doped N-type regions 682 andheavily doped P-type regions 684 in the SRAM array 600 shown in FIG. 6A(or FIG. 6B), in accordance with some embodiments. In addition, FIG. 9illustrates the arrangements of the heavily doped N-type regions 682 andthe heavily doped P-type regions 684 in the bit cell array 602A, the bitcell array 602B and the strap cell 604 of the SRAM array 600.

In some embodiments, the SRAM array 600 includes the heavily dopedN-type regions 682 and the heavily doped P-type regions 684. Each of theheavily doped N-type regions 682 and the heavily doped P-type regions684 may have a strip-shape extending along the direction 302 (e.g. thecolumn direction). In addition, the heavily doped N-type regions 682 andthe heavily doped P-type regions 684 may be arranged alternately alongthe direction 300 (e.g. the row direction).

In the strap cell 604, two of the heavily doped N-type regions 682 arepositioned overlying the strip portions 672-1 and 672-2 of the H-shapedPW region 670 (FIG. 6A), in accordance with some embodiments shown inFIG. 9. Another of the heavily doped N-type regions 682 may bepositioned overlying the linking portion 664 of the H-shaped NW region660 and the PW regions 676 and 677 (FIG. 6A). In addition, other two ofthe heavily doped N-type regions 682 may be positioned overlying thehorizontal portion 678-1 of the T-shaped PW region 678 and thestrip-shaped PW region 679 (FIG. 6A). Furthermore, NW contacts 686 maybe positioned on the heavily doped N-type region 682 overlying thelinking portion 664 of the H-shaped NW region 660 (FIG. 6A).

Because the H-shaped NW region 660 and the NW regions 666, 667, 668 and669 are electrically connected to each other by the DNW region 680 (FIG.7A), the NW contacts 686 may serve as contacts of the H-shaped NW region660 and the NW regions 666, 667, 668 and 669.

In the strap cell 604, two of the heavily doped P-type regions 684 arepositioned overlying the strip portions 662-1 and 662-2 of the H-shapedNW region 660 (FIG. 6A), in accordance with some embodiments shown inFIG. 9. Another of the heavily doped P-type regions 684 may bepositioned overlying the linking portion 674 of the H-shaped PW region670 and the NW regions 666 and 667 (FIG. 6A). In addition, yet anotherof the heavily doped P-type regions 684 may be positioned overlying thevertical portion 678-2 of the T-shaped PW region 678 (FIG. 6A).Furthermore, PW contacts 688 may be positioned on the heavily dopedP-type regions 684 overlying the strip portions 672-1 and 672-2 of theH-shaped PW region 670 (FIG. 6A).

Because the H-shaped PW region 670, the PW region, 676 and 677, theT-shaped PW region 678 and the strip-shaped PW region 679 areelectrically connected to each other (FIG. 7B), the PW contacts 688 mayserve as contacts of the H-shaped PW region 670, the PW region, 676 and677, the T-shaped PW region 678 and the strip-shaped PW region 679.

In some embodiments, the heavily doped N-type regions 682 are positionedoverlying the PW regions 254 in the bit cell array 602A and the bit cellarray 602B. The heavily doped P-type regions 684 may be positionedoverlying the NW regions 252 in the bit cell array 602A and the bit cellarray 602B.

In some embodiments, the strap cell 604 of the SRAM array 600 includesdiscrete NW regions and PW regions arranged alternately along thedirection 300 (the row direction) and along the direction 302 (thecolumn direction). The NW regions (or the PW regions) positioned in thestrap cell 604 and close to the boundary 681 of the DNW region 680 maydirectly connect to the corresponding NW regions 252 (or thecorresponding PW regions 254) in the bit cell array 602A and the bitcell array 602B. For example, the discrete NW regions in the strap cell604 may include the H-shaped NW region 660 and NW regions 666, 667, 668and 669. The discrete PW regions in the strap cell 604 may include theH-shaped PW region 670, the T-shaped PW region 678, the strip-shaped PWregion 679 and the discrete PW regions 676 and 677. In addition, thediscrete NW regions 666, 667, 668 and 669 may be connected to each otherthrough the DNW region 680 underlying the NW regions. Therefore, thenumber of NW pick-up regions (the NW contacts 686) may be reduced.Furthermore, the strap cell and the bit cell array may have the samearrangements of the heavily doped N-type regions and the heavily dopedP-type regions. For example, the heavily doped N-type (N+) regions 682and the heavily doped P-type (P+) regions 684 in the strap cell 604 andthe bit cell arrays 602A and 602B may be arranged extending along thedirection 302 (the column direction) and alternately along the direction300 (the row direction). The length of the strap cell 604 along thedirection 302 may be further reduced. For example, the length of thestrap cell 604 may be reduced equal to or less than six times as largeas the poly height (also referred to as poly (gate) pitch (i.e. thelength of poly (gate) to poly (gate) within a regular pattern).Therefore, the distance between the well pick-up region (e.g., the PWcontact or the NW contact) and the corresponding well regions (e.g., theNW regions 252 or the PW regions 254) in the SRAM cell 500 in the bitcell array (602A or 602B) may be reduced. The resistance of the wellregions may be reduced. The latch-up problem may be avoided.

As described previously, embodiments of a static random access memory(SRAM) array 600 are provided. In some embodiments, the strap cell 604of the SRAM array 600 includes the H-shaped NW region 660, the H-shapedPW region 670 and the deep N-type well (DNW) region 680. The H-shaped NWregion 660 and the H-shaped PW region 670 each includes two stripportions (e.g., the strip portions 662-1, 662-2, 672-1 and 672-2)extending along the first direction (e.g., the direction 302) and thelinking portion (e.g., the linking portions 664 and 674) extending alongthe second direction (e.g., the direction 300). Two terminals (e.g., theterminals 664-1, 664-2, 674-1 and 674-2) of the linking portion are incontact with the two strip portions. In some embodiments, the strap cell604 of the SRAM array 600 includes a first strap column 630, a firststrap row 642 and a deep N-type well (DNW) region 680. The first strapcolumn 634 includes a first P-type well (PW) region (e.g., the linkingportion 674 of the H-shaped PW region 670) and a first N-type well (NW)region (e.g., the NW region 666) and a second NW region (e.g., the NWregion 667) on opposite sides of the first PW region along the firstdirection (e.g., the direction 302). The first strap row 642 includesthe first NW region (e.g., the NW region 666) and a second PW region(e.g., a portion of the PW region 672-1) and a third PW region (e.g., aportion of the PW region 672-2) on opposite sides of the first NWregion. The deep N-type well (DNW) region 680 is positioned underlyingand connected to the first NW region and the second NW region of thefirst strap column. The arrangements of the NW regions and the PWregions of the strap cell 604 may reduce the area of the strap cell. Theresistance of the well regions may be reduced. The latch-up problem maybe avoided.

Embodiments of a static random access memory (SRAM) array are provided.The SRAM array is positioned between a first bit cell array and a secondbit cell array along a first direction and is arranged along a seconddirection. The strap cell includes an H-shaped NW region, an H-shaped PWregion and a deep N-type well (DNW) region. The H-shaped NW region andthe H-shaped PW region each includes two strip portions extending alongthe first direction and a linking portion extending along the seconddirection. The distance between the well pick-up region and thecorresponding well regions in the SRAM cell in the bit cell array may bereduced. The resistance of the well regions may be reduced. The latch-upproblem may be avoided.

In some embodiments, a static random access memory (SRAM) array includesa first bit cell array, a second bit cell array and a strap cell. Thesecond bit cell array is arranged along a first direction. The strapcell is arranged along a second direction and is positioned between thefirst bit cell array and the second bit cell array along the firstdirection. The strap cell includes an H-shaped NW region, an H-shaped PWregion and a deep N-type well (DNW) region. The H-shaped NW region andthe H-shaped PW region each includes two strip portions extending alongthe first direction and a linking portion extending along the seconddirection. Two terminals of the linking portion are in contact with thetwo strip portions.

In some embodiments, a static random access memory (SRAM) array includesa first bit cell array, a second bit cell array and a strap cell. Thesecond bit cell array is arranged along a first direction. The strapcell is arranged along a second direction and is positioned between thefirst bit cell array and the second bit cell array along the firstdirection. The strap cell includes a first strap column, a first straprow and a deep N-type well (DNW) region. The first strap column includesa first P-type well (PW) region and a first N-type well (NW) region anda second NW region on opposite sides of the first PW region along thefirst direction. The first strap row includes the first NW region and asecond PW region and a third PW region on opposite sides of the first NWregion. The deep N-type well (DNW) region is positioned underlying andconnected to the first NW region and the second NW region of the firststrap column.

In some embodiments, a static random access memory (SRAM) array includesa first bit cell array, a second bit cell array and a strap cell. Thefirst bit cell array and the second bit cell array are arranged along afirst direction. The first bit cell array and the second bit cell arrayeach includes a plurality of functional SRAM cells. The strap cell isarranged in a second direction and is positioned between the first bitcell array and the second bit cell array along the first direction. Thestrap cell includes a first strap column, a second strap column, aheavily doped P-type region, a heavily doped N-type region and a deepN-type well (DNW) region. The first strap column includes a first P-typewell (PW) region and two first N-type well (NW) regions adjacentopposite sides of the first PW region along the first direction. Thesecond strap column is positioned adjacent to the first strap columnalong the second direction. The second strap column includes a second NWregion and two second PW regions adjacent opposite sides of the secondNW region along the first direction. The heavily doped P-type region ispositioned overlying the first PW region and the two first NW regions ofthe first strap column. The heavily doped N-type region is positionedoverlying the second NW region and the two second PW regions of thesecond strap column. The deep N-type well (DNW) region is positionedunderlying the two first NW regions and the second NW region.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A static random access memory (SRAM) array,comprising: a first bit cell array and a second bit cell array arrangedalong a first direction; a strap cell arranged along a second directionand positioned between the first bit cell array and the second bit cellarray along the first direction, wherein the strap cell comprises: anH-shaped NW region; an H-shaped PW region adjacent to the H-shaped NWregion along the second direction, wherein the H-shaped NW region andthe H-shaped PW region each comprises: two strip portions extendingalong the first direction; and a linking portion extending along thesecond direction, wherein two terminals of the linking portion are incontact with the two strip portions; and a deep N-type well (DNW) regionunderlying the H-shaped NW region and the H-shaped PW region.
 2. TheSRAM array as claimed in claim 1, wherein the strap cell comprises: afirst PW region and a second PW region adjacent to opposite sides of thelinking portion of the H-shaped NW region along the first direction; anda first NW region and a second NW region adjacent to opposite sides ofthe linking portion of the H-shaped PW region along the first direction.3. The SRAM array as claimed in claim 2, wherein the strap cellcomprises: a first heavily doped P-type region overlying the two stripportions of the H-shaped NW region; and a first heavily doped N-typeregion overlying the linking portion of the H-shaped NW region and thetwo PW regions.
 4. The SRAM array as claimed in claim 2, wherein thestrap cell comprises: a second heavily doped N-type region overlying thetwo strip portions of the H-shaped PW region; and a second heavily dopedP-type region overlying the linking portion of the H-shaped PW regionand the two NW regions.
 5. The SRAM array as claimed in claim 2, whereinthe first bit cell array and the second bit cell array each comprises:third NW regions extending along the column region; and third PW regionsextending along the column region, wherein the third NW regions and thethird PW regions are arranged alternately along the second direction. 6.The SRAM array as claimed in claim 5, wherein the first PW region andthe second PW region of the strap cell are respectively in directcontact with the corresponding third PW region of the first bit cellarray and the corresponding third PW region of the second bit cellarray.
 7. The SRAM array as claimed in claim 5, wherein the first NWregion and the second NW region of the strap cell are respectively indirect contact with the corresponding third NW region of the first bitcell array and the corresponding third NW region of the second bit cellarray.
 8. The SRAM array as claimed in claim 1, wherein the first bitcell array and the second bit cell array each comprises a plurality ofSRAM cells, wherein some of the SRAM cells in the column share a bitline (BL).
 9. The SRAM array as claimed in claim 8, wherein each of theSRAM cells in the first bit cell array and the second bit cell array hasa pitch along the second direction, wherein the total width of theH-shaped NW region and the H-shaped PW region along the second directionis three times as long as the pitch.
 10. A static random access memory(SRAM) array, comprising: a first bit cell array and a second bit cellarray arranged along a first direction; a strap cell arranged along asecond direction and positioned between the first bit cell array and thesecond bit cell array along the first direction, wherein the strap cellcomprises: a first strap column, comprising: a first P-type well (PW)region; and a first N-type well (NW) region and a second NW regionadjacent to opposite sides of the first PW region along the firstdirection; a first strap row, comprising: the first NW region; and asecond PW region and a third PW region on opposite sides of the first NWregion; and a deep N-type well (DNW) region underlying and connected tothe first NW region and the second NW region of the first strap column.11. The SRAM array as claimed in claim 10, wherein the strap cellcomprises: a second strap column comprising the second PW region,wherein the length of the second PW region is equal to the length of thesecond strap column along the first direction; and a third strap columncomprising the third PW region, wherein the length of the third PWregion is equal to the length of the third strap column along the firstdirection.
 12. The SRAM array as claimed in claim 11, wherein the widthsof the second strap column and the third strap column are greater thanthe width of the first strap column along the second direction.
 13. TheSRAM array as claimed in claim 11, wherein the first PW region of thefirst strap column is directly connected to the second PW region of thesecond strap column and the third PW region of the third strap column toform an H-shaped PW region in a plan view.
 14. The SRAM array as claimedin claim 10, wherein the first strap row of the strap cell comprises: afourth PW region; and a third NW region and a fourth NW region onopposite sides of the fourth PW region along the second direction. 15.The SRAM array as claimed in claim 14, wherein the strap cell comprises:a fourth strap column, comprising: a fifth NW region; and the fourth PWregion and a sixth PW region on opposite sides of the first PW regionalong the first direction; a fifth strap column comprising the third NWregion, wherein the length of the third NW region is equal to the lengthof the fifth strap column; and a sixth strap column comprising thefourth NW region, wherein the length of the fourth NW region is equal tothe length of the sixth strap column.
 16. The SRAM array as claimed inclaim 15, wherein the fifth NW region of the fourth strap column isdirectly connected to the third NW region of the fifth strap column andthe fourth NW region of the sixth strap column to form an H-shaped NWregion in a plan view.
 17. The SRAM array as claimed in claim 15,wherein the width of the fourth strap column is greater than the widthsof the fifth strap column and the sixth strap column along the seconddirection.
 18. A static random access memory (SRAM) array, comprising: afirst bit cell array and a second bit cell array arranged along a firstdirection; a strap cell arranged in a second direction and positionedbetween the first bit cell array and the second bit cell array along thefirst direction, wherein the strap cell comprises: a first strap columncomprising a first P-type well (PW) region and two first N-type well(NW) regions adjacent opposite sides of the first PW region along thefirst direction; and a second strap column adjacent to the first strapcolumn along the second direction, wherein the second strap columncomprises: a second NW region and two second PW regions adjacentopposite sides of the second NW region along the first direction; aheavily doped P-type region overlying the first PW region and the twofirst NW regions of the first strap column; a heavily doped N-typeregion overlying the second NW region and the two second PW regions ofthe second strap column; and a deep N-type well (DNW) region underlyingthe two first NW regions and the second NW region.
 19. The SRAM array asclaimed in claim 18, wherein the two first NW regions of the first strapcolumn of the first strap cell respectively connected to an NW region ofthe first bit cell array and an NW region of the second bit cell arrayalong the first direction.
 20. The SRAM array as claimed in claim 18,wherein the two second PW regions of the second strap column of thefirst strap cell are respectively connected to a PW region of the firstbit cell array and a PW region of the second bit cell array along thefirst direction.